2. Idealism: everything is mental. Pan-psychism: everything is conscious, at
least to a degree.

3. Identity theory: mental state = brain state. E.g. JJC Smart 1950s

4. Functionalism: mental state = functional state of an information processing
system. There is an underlying physical state (functionalism is a kind of materialism)
but the physical state places no constraints on mental states.

5. Eliminative materialism: do not try to equate mental states with anything,
since our theory of mental states is just part of folk psychology which is largely
false. Instead, replace talk of mental states with theories drawn from human
neuroscience. Reject functionalism because it is crucial that thinking is based
in human brains. Paul and Pat Churchland.

6. Mysterian materialism: mental states are physical states, but are far too
weird and complicated to be explained scientifically.